Cooling device and construction machine or working machine equipped with the same

ABSTRACT

A cooling device includes: a cooling fan; a shroud provided at an outer circumferential side of the cooling fan; an inner circumferential wall provided on the shroud and adjacent to the outer circumference of the cooling fan so as to surround the cooling fan; an outer circumferential wall provided to surround the inner circumferential wall. An air-flow-direction downstream side end of the outer circumferential wall is positioned at a further downstream position in an air flow direction than an air-flow-direction downstream side end of the inner circumferential wall. The cooling fan is rotatable within a space provided on a radially inner side of the inner circumferential wall. The air-flow-direction downstream side end of the outer circumferential wall is provided at a further upstream position in the air flow direction than an air-flow-direction downstream side end of the cooling fan.

TECHNICAL FIELD

The present invention relates to a cooling device and a constructionmachine or work machine including the same. More particularly, thepresent invention relates to a cooling device including a cooling fanand a shroud surrounding the cooling fan, and a construction machine orwork machine including the same.

BACKGROUND ART

Traditionally, a cooling system of an engine installed in a constructionmachine mainly includes a radiator and a cooling fan. The radiatorcirculates cooling medium between the radiator and the engine and coolsthe cooling medium by outer air. The cooling fan forms air flow aroundthe radiator and aids heat exchange of the radiator. Further, a shroudis provided between the radiator and the cooling fan to surround theradiator and the cooling fan for ensuring air flow from the radiator tothe cooling fan (for example, see Patent Document 1).

In recent years, the total heat quantity of an engine is increased andtherefore the water temperature of a radiator is increased. To solvesuch a problem, for example, the flow of air blown by a cooling fan(i.e., the flow of air passing through the vicinity of the radiator) maybe increased by increasing the rotation speed of the cooling fan.However, when the rotation speed of the cooling fan is increased, noiseis increased.

Accordingly, to enhance cooling capability of a cooling system of theengine, it is required to increase the flow of air blown by the coolingfan without increasing the rotation speed of the cooling fan. Varioustechnologies for changing a shape and position of a shroud have beendeveloped. For example, to prevent counter flow of air discharged fromthe cooling fan (i.e., to prevent air in the engine from returning tothe radiator through the cooling fan), two cylindrical portions areprovided on an end of the shroud (for example, see Patent Document 2).

Patent Document 1: JP-A-9-118141 (Published on May 6, 1997)

Patent Document 2: JP-A-2006-132380 (Published on May 25, 2006)

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

However, according to the cooling system of the engine disclosed inPatent Document 1, the cooling fan is completely accommodated in theshroud. Accordingly, the flow of air discharged from the cooling fan isnot sufficiently increased.

Also, according to the cooling system of the engine disclosed in PatentDocument 2, the entire cooling fan is provided outside of the shroud.Accordingly, the flow of air discharged from the cooling fan is notrarely affected by the cylindrical portions of the shroud. Thus, theflow of air discharged from the cooling fan is not sufficientlyincreased.

An object of the invention is to provide a cooling device capable ofsufficiently increasing flow of air from a cooling fan withoutincreasing rotation speed of the cooling fan, and to provide aconstruction machine or work machine equipped with the cooling device.

Means for Solving the Problems

A cooling device according to an aspect of the invention includes: acooling fan; a shroud provided at an outer circumferential side of thecooling fan; an inner circumferential wall provided on the shroud andadjacent to the outer circumference of the cooling fan so as to surroundthe cooling fan; and an outer circumferential wall provided to surroundthe inner circumferential wall, an air-flow-direction downstream sideend of the outer circumferential wall being positioned at a furtherdownstream position in an air flow direction than an air-flow-directiondownstream side end of the inner circumferential wall, in which thecooling fan is rotatable in a space on a radially inner side of theinner circumferential wall, and the air-flow-direction downstream sideend of the outer circumferential wall is positioned at a furtherupstream position in the air flow direction than an air-flow-directiondownstream side end of the cooling fan.

The inner circumferential wall and the outer circumferential wall may beprovided by arranging a plurality of members around a rotation shaft ofthe cooling fan. However, it is preferable that at least either one ofthe inner circumferential wall and the outer circumferential wall is aring that is consecutively provided around the rotation shaft of thecooling fan.

In the cooling device according to the aspect of the invention, when thecooling fan is rotated and an air flow is generated, a negative pressuregenerated in a space between the inner circumferential wall and outercircumferential wall of the ring suctions the air into the space, or thesuctioned air is swept out from the space. With this arrangement, theflow of air blown by the cooling fan is increased. Thus, coolingcapability is enhanced even when the rotation speed of the cooling fanremains the same as conventional. Even when the rotation speed of thecooling fan is reduced, the same cooling capability can be obtained.

Preferably in the cooling device according to the aspect of theinvention, an exterior covering ratio is in a range of 55 to 95%, theexterior covering ratio being defined as a ratio between: anair-flow-direction length of a portion covered by the shroud and theouter circumferential wall; and a maximum air-flow-direction length ofthe cooling fan in the air flow direction of the cooling fan. Theexterior covering ratio is more preferably 70 to 95%, further morepreferably 70 to 80%.

Since the exterior covering ratio is set in the range of 55 to 95% inthe cooling device according to the aspect of the invention, the flow ofair blown by the cooling fan is sufficiently increased. Thus, coolingcapability is enhanced even when the rotation speed of the cooling fanremains the same as conventional. Even when the rotation speed of thecooling fan is reduced, the same cooling capacity can be obtained. It ismore preferable that the exterior covering ratio is 70 to 95% to reducethe noise. It is also more preferable that the exterior covering ratiois 70 to 80% to enhance the cooling capability by increasing the windflow.

Preferably in the cooling device according to the aspect of theinvention, an interior covering ratio is in a range of 45 to 85%, theinterior covering ratio being defined as a ratio between: anair-flow-direction length of a portion covered by the shroud and theinner circumferential wall; and a maximum air-flow-direction length ofthe cooling fan in the air flow direction of the cooling fan.

Since the interior covering ratio is set in the range of 45 to 85% inthe cooling device according to the aspect of the invention, the flow ofair blown by the cooling fan is sufficiently increased. Thus, coolingcapability is enhanced even when the rotation speed of the cooling fanremains the same as conventional. Even when the rotation speed of thecooling fan is reduced, the same cooling capability can be obtained.

Preferably in the cooling device according to the aspect of theinvention, at least one of the inner circumferential wall and the outercircumferential wall may be integrated with the shroud.

To integrally form at least either one of the inner circumferential walland the outer circumferential wall with the shroud, at least either oneof the shroud and the inner circumferential wall and outercircumferential wall may be made of resin and formed integrally byinjection molding.

In such a cooling device, the load of assembling work can be reduced byreduction of the number of parts because at least one of the innercircumferential wall and the outer circumferential wall is integratedwith the shroud.

Preferably in the cooling device according to the aspect of theinvention, at least one of the inner circumferential wall and the outercircumferential wall is formed by a member different from the shroud.

In such a cooling device, the inner circumferential wall and the outercircumferential wall can be appropriately selected suitably for thearrangement of the shroud and the cooling fan because at least eitherone of the inner circumferential wall and the outer circumferential wallis attachable to the shroud.

The cooling device according to the aspect of the invention preferablyfurther includes an annular base connecting the inner circumferentialwall to the outer circumferential wall.

It is easy to manufacture and manage such a cooling device owing to theuse of single integrated member formed by the inner circumferentialwall, the outer circumferential wall and the base.

Preferably in the cooling device according to the aspect of theinvention, at least one of the inner circumferential wall and the outercircumferential wall includes a cylindrical portion extending inparallel to the air flow direction.

According to such a cooling device, it is easy to manufacture the innercircumferential wall and the outer circumferential wall because at leastone of the inner circumferential wall and the outer circumferential wallhas a cylindrical portion extending in parallel to the air flowdirection.

Preferably in the cooling device according to the aspect of theinvention, at least one of the inner circumferential wall and the outercircumferential wall includes a diameter-expanded portion of which aninner diameter increases toward downstream in the air flow direction.

Since at least one of the inner circumferential wall and the outercircumferential wall has the diameter-expanded portion in such a coolingdevice, the flow of air blown by the cooling fan is sufficientlyincreased.

A construction machine or a work machine according to another aspect ofthe invention includes any one of the above-described cooling devices.

Since the construction machine or the work machine includes the coolingdevice capable of enhancing the cooling efficiency, the constructionmachine or the work machine can ensure a highly quiet operation byreducing operational noise generated by the cooling fan.

In the cooling device according to the aspect of the invention, the flowof air blown by the cooling fan can be sufficiently increased withoutincreasing the rotation speed of the cooling fan.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an overall view showing a hydraulic excavator including ashroud structure of a cooling fan according to an exemplary embodimentof the invention.

FIG. 2 is a perspective view showing an arrangement in the vicinity ofan engine room and a counterweight mounted on a rear side of thehydraulic excavator.

FIG. 3 is a perspective view showing an engine hood in an open state,the engine hood provided on an upper surface of the engine room shown inFIG. 2.

FIG. 4 is a plain view showing an arrangement within the engine hoodshown in FIG. 3.

FIG. 5 is a partially enlarged view of FIG. 4.

FIG. 6 is a perspective view showing an arrangement of a cooling unit.

FIG. 7 schematically shows a relationship of an engine and the coolingunit.

FIG. 8 is a cross-sectional view showing a positional relationship of aring and an outer circumference of the cooling fan.

FIG. 9 is a schematic view for explaining effect of increase in windflow by the ring.

FIG. 10 is a graph showing a relationship between an interior coveringratio and a wind flow.

FIG. 11 is a graph showing a relationship between air-flow-directionlengths of an inner circumferential wall and an outer circumferentialwall, wind flow and noise.

FIG. 12 is a graph showing a relationship between an exterior coveringratio and wind flow.

FIG. 13 is a graph showing a relationship between an exterior coveringratio and noise.

FIG. 14A is a schematic view for explaining a positional relationshipbetween an air-flow-direction downstream side end of the cooling fan andan air-flow-direction downstream side end of the outer circumferentialwall and the principle of generation of negative pressure.

FIG. 14B is a schematic view for explaining the positional relationshipbetween the air-flow-direction downstream side end of the cooling fanand the air-flow-direction downstream side end of the outercircumferential wall and the principle of generation of negativepressure.

FIG. 15 is a front view showing an arrangement of an innercircumferential wall and an outer circumferential wall of a cooling fanaccording to a second exemplary embodiment of the invention.

FIG. 16 is a front view showing an arrangement of a ring according toanother exemplary embodiment.

FIG. 17 is a cross-sectional view showing an arrangement of a ringaccording to another exemplary embodiment.

FIG. 18 is a cross-sectional view showing an arrangement of a ringaccording to another exemplary embodiment.

FIG. 19 is a cross-sectional view showing an arrangement of a ringaccording to another exemplary embodiment.

FIG. 20 is a cross-sectional view showing an arrangement of a ringaccording to another exemplary embodiment.

FIG. 21 is a cross-sectional view showing an arrangement of a ringaccording to another exemplary embodiment.

FIG. 22 schematically shows a relationship between an engine and acooling unit when the invention is applied to a blowoff cooling unit.

EXPLANATION OF CODES

1 . . . hydraulic excavator, 2 . . . undercarriage, 3 . . . swing frame,4 . . . working equipment, 5 . . . counterweight, 6 . . . engine room, 6a . . . engine, 9 . . . equipment enclosure, 10 . . . cab, 11 . . .boom, 11 a, 12 a, 13 a . . . hydraulic cylinder, 12 . . . arm, 13 . . .bucket, 14 . . . engine hood, 14 a . . . grab, 20 . . . cooling unit, 21. . . cooling fan, 21 a . . . vane, 30 . . . cooling core, 31 . . .radiator, 32 . . . oil cooler, 33 . . . aftercooler, 35 . . . aircleaner, 40 . . . shroud, 41 . . . case, 51 . . . ring, 52 . . . innercircumferential wall, 53 . . . outer circumferential wall, 54 . . .base, 55 . . . space, 61 . . . ring, 62 . . . inner circumferentialwall, 63 . . . outer circumferential wall, 64 . . . base, 65 . . .space, 71 . . . ring, 72 a, 73 a . . . taper portion, 72 . . . innercircumferential wall, 73 . . . outer circumferential wall, 74 . . .base, 75 . . . space, 81 . . . ring, 82 . . . inner circumferentialwall, 82 a . . . cylindrical portion, 82 b . . . fixed portion, 83 . . .outer circumferential wall, 83 a . . . tubular potion, 83 b . . . fixedportion, 85 . . . space, 91 . . . ring, 92 . . . inner circumferentialwall, 93 . . . outer circumferential wall, 93 a . . . cylindricalportion, 93 b . . . fixed portion, 95 . . . space, 101 . . . ring, 102 .. . inner circumferential wall, 103 . . . outer circumferential wall,105 . . . space, P . . . crawler belt, 112 . . . wall component, 113 . .. semi-annular member

BEST MODE FOR CARRYING OUT THE INVENTION

As an exemplary embodiment of the invention, a hydraulic excavator(construction machine) 1 including a cooling unit 20 (a cooling deviceaccording to the aspect of the invention) will be described below withreference to the accompanying drawings.

First Exemplary Embodiment

[Entire Arrangement of Hydraulic Excavator 1]

As shown in FIG. 1, a hydraulic excavator 1 according to a firstexemplary embodiment includes: an undercarriage 2; a swing frame 3; aworking equipment 4; a counterweight 5; an engine room 6; an equipmentenclosure 9; a cab 10; and a cooling unit 20 (see FIG. 3).

The undercarriage 2 moves the hydraulic excavator 1 forward and backwardby rotating crawler belts P wound around right and left ends in thetraveling direction while carrying the swing frame 3 in a mannerswingable on an upper surface of the undercarriage 2.

The swing frame 3 is swingable in any direction on the undercarriage 2.The working equipment 4, counterweight 5, engine room 6 and cab 10 areprovided on an upper surface of the swing frame 3.

The working equipment 4 includes: a boom 11; an arm 12 provided on anend of the boom 11; and a bucket 13 provided on an end of the arm 12.The working equipment 4 is used to excavate gravel and sand at a site ofcivil engineering works by moving the boom 11, arm 12 and bucket 13 upand down using hydraulic cylinders 11 a, 12 a and 13 a included in ahydraulic circuit (not shown).

The counterweight 5, which is made by solidifying scrap iron andconcrete poured into a box formed by steel plates, is provided on a rearside of the engine room 6 on the swing frame 3 to balance the vehiclebody during mining.

As shown in FIGS. 2 and 3, the engine room 6 is adjacent to thecounterweight 5. The engine room 6 has an upper opening for inspectioncovered by an engine hood 14 openable and closable by a grab 14 a. Theengine room 6 accommodates a cooling unit 20 including: an engine 6 a asa power source for driving the undercarriage 2 and the working equipment4; and a cooling core 30 (see FIG. 3).

The equipment enclosure 9 is provided on a rear side of the workingequipment 4 and includes a fuel tank, hydraulic oil tank and operationvalve (not shown) therein.

The cab 10, which is a room for an operator of the hydraulic excavator1, is provided on a front and left side on the swing frame 3 (a side ofthe working equipment 4) so that the operator can see a distal end ofthe working equipment 4.

As shown in FIG. 4, the cooling unit 20 is adjacent to the engine 6 a inthe engine room 6 to cool cooling water and hydraulic oil flowingthrough the engine 6 a. The arrangement of the cooling unit 20 will bedescribed later in detail.

[Cooling Unit 20]

As shown in FIGS. 3 and 4, the cooling unit 20 includes a cooling fan 21and the cooling core 30. The cooling unit 20 also includes thelater-described shroud 40 (see FIG. 6) to send a large volume of air tothe cooling core 30 for efficient cooling while reducing the noise.

As shown in FIG. 6, the cooling fan 21 is directly connected to theengine 6 a. Vanes 21 a (see FIG. 6) are rotated directly by the engine 6a. In this exemplary embodiment, when the cooling fan 21 is driven, airflows in a direction where the cooling fan 21 suctions the air as arrowsF in FIGS. 4, 7 and 8 indicate. In other words, the cooling fan 21 islocated on the downstream side of the cooling core 30 in the air flowgenerated by the cooling fan 21. The arrangement of the cooling fan 21will be described later in detail. Hereinafter, the direction indicatedby the arrows F in FIGS. 4, 7 and 8 will be referred to as an air flowdirection. The left side and right side in FIGS. 4, 7 and 8 will bereferred to respectively as an upstream side and a downstream side.

The cooling core 30 is a unit for cooling the cooling medium by heatexchange with air. As shown in FIG. 5, the cooling core 30 includes aradiator 31, an oil cooler 32 and an aftercooler 33.

The radiator 31 reduces the temperature of cooling water flowing throughthe engine 6 a by heat exchange between the cooling water and airgenerated by the cooling fan 21.

The oil cooler 32 reduces the temperature of oil to be delivered to thehydraulic cylinders 11 a, 12 a and 13 a by heat exchange between oilsupplied from the hydraulic oil tank to the hydraulic circuit and heatedand air generated by the cooling fan 21.

The aftercooler 33 cools the heated air by heat exchange between airsuctioned from an air cleaner 35 and discharged from a turbocharger (notshown) of the engine 6 a and air generated by the cooling fan 21, andthen delivers the cooled air to an intake manifold (not shown) of theengine 6 a.

[Cooling Fan 21]

The cooling fan 21 is an axial-flow fan having a plurality of vanes 21 arotatable around a rotation shaft and driven by the engine 6 a. Thenumber of the vanes 21 a depends on an airflow volume and a size of thecooling fan 21. Typically, the number of the vanes 21 a is approximately6 to 11.

The vanes 21 a are rotated by the engine 6 a. By rotating the pluralityof vanes 21 a, the generated air flow flows radially outward from therotation shaft.

As shown in FIGS. 6 to 8, the shroud 40 covers an outer circumference ofthe vanes 21 a of the cooling fan 21 and includes a case 41. The case 41is a plate-shaped member having a circular opening conformed to theouter circumference of the vanes 21 a.

A ring 51 is fixed to an inner circumference of the case 41. The ring51, which is for increasing the flow of air blown by the cooling fan 21,is made of sheet-metal or resin.

As shown in FIG. 8, the ring 51 includes an inner circumferential wall52, an outer circumferential wall 53 and a base 54.

The inner circumferential wall 52 is positioned on an edge of theopening of the case 41 and is adjacent to an outer circumferential edgeof (the vanes 21 a of) the cooling fan 21. The diameter of the innercircumferential wall 52 is larger than the outer diameter of the coolingfan 21. A clearance G between the inner circumferential wall 52 and thecooling fan 21 is, for example, 15 mm.

The outer circumferential wall 53 is positioned at a further radiallyoutward position than the inner circumferential wall 52 to surround theinner circumferential wall 52. An annular space 55 is providedtherebetween. The inner circumferential wall 52 and the outercircumferential wall 53 are concentrically-positioned cylindricalmembers and extend in parallel in the air flow direction.

In the first exemplary embodiment, no bore is formed on the innercircumferential wall 52 or the outer circumferential wall 53. Anair-flow-direction length h1 of the inner circumferential wall 52 issmaller than an air-flow-direction length h2 of the outercircumferential wall 53. In other words, an air-flow-directiondownstream side end of the outer circumferential wall 53 is positionedat a further downstream position in the air flow direction than anair-flow-direction downstream side end of the inner circumferential wall52.

The base 54 is annular and flat to connect the outer circumferentialwall 53 with the inner circumferential wall 52. As described above, thering 51 is a single member and attachable to the case 41. The ring 51may include fixed portions (not shown). For example, the fixed portionsmay be projections extending radially outward from the base at aplurality of positions in the circumferential direction. The ring 51 maybe fixed to the case 41 by weld, adhesion or any other fixing member.

In the first exemplary embodiment, the air-flow-direction length h1 ofthe inner circumferential wall 52 is 20 mm, the air-flow-directionlength h2 of the outer circumferential wall 53 is 30 mm, and a width Wof the base 54 is 30 mm. However, the invention is not limited to thesenumerical values.

Next, a positional relationship of the cooling fan 21 and the ring 51will be described below. As shown in FIG. 8, the outer circumferentialedge of the cooling fan 21 is positioned at a further downstreamposition in the air flow direction than the inner circumferential wall52 of the ring 51.

More specifically, the air-flow-direction downstream side end of theouter circumferential edge of the cooling fan 21 is positioned at afurther downstream position in the air flow direction than theair-flow-direction downstream side end of the inner circumferential wall52.

An air-flow-direction length of the cooling fan 21 will be referred toas h3. An air-flow-direction length of an upstream portion of thecooling fan 21, which is positioned at a further upstream position thanthe end of the inner circumferential wall 52, will be referred to as h4.

A percentage of h4/h3 will be referred to as an “interior covering ratio(%).” For example, the interior covering ratio is 62.5% in the firstexemplary embodiment.

[Cooling Operation]

When the cooling fan 21 is driven by the engine 6 a, air in the vicinityof the cooling core 30 is suctioned into the cooling fan 21. This flowof the air cools down the radiator 31 and the like of the cooling core30.

As shown in FIG. 9 (A), when a vane 21 a of the cooling fan 21 passesthrough a position P1 in the space 55 (an observation point in FIG. 9),air in the vicinity of the P1 is swept out by flow of air from the vane21 a, such that negative pressure is generated at the P1. Next, as shownin FIG. 9 (B), when the P1 in the space 55 (the observation point inFIG. 9) is positioned between vanes 21 a of the cooling fan 21, thenegative pressure generated at the P1 suctions the air and suppressesthe generation of vortex. Due to such a phenomenon, flow of air blown bythe cooling fan 21 is considerably increased as compared with aconventional arrangement.

Consequently, an amount of air supplied to the cooling core 30 isincreased, so that cooling efficiency can be enhanced.

With such an arrangement according to the aspect of the invention, thenegative pressure generated in the space 55 can suppress the generationand growth of Karman vortex, and thus the noise is considerably reducedas compared to a conventional arrangement. Accordingly, even when therotation speed of the cooling fan 21 is increased to be more than therotation speed of a conventional cooling fan, the noise is still in atolerable range.

Especially, in this exemplary embodiment, since the air-flow-directiondownstream side end of the cooling fan 21 is positioned at a furtherdownstream position in the air flow direction than theair-flow-direction downstream side end of the inner circumferential wall52 of the ring 51, the flow of air is further increased due to theabove-described phenomenon. This is presumably because air in the space55 can be more effectively swept out when the vane 21 passes by in theabove-described structure.

[Relationship Between Covering Ratio and Wind Flow]

Initially, the interior covering ratio of the inner circumferential wall52 was changed in the cooling fan 21 having the same rotation speed tomeasure the change of flow of air blown by the cooling fan 21. When theinterior covering ratio was 100%, the wind flow was small as shown inFIG. 10. The wind flow was gradually increased as the interior coveringratio was reduced. The wind flow reached its peak when the interiorcovering ratio was appropriately 60 to 70%. When the interior coveringratio was further reduced, the wind flow was reduced. When the interiorcovering ratio was less than 45% or more than 85%, the wind flow wasalmost equal to the wind flow exhibited when the interior covering ratiowas 100%. In FIG. 10, a scale unit of the vertical axis of the graph is10 m³/min.

From the above, it was found that a sufficient wind flow was obtainedwhen the interior covering ratio was in the range of 45 to 85%.

The air-flow-direction lengths h1 and h2 of the inner circumferentialwall 52 and the outer circumferential wall 53 were changed to differfrom each other by 0 mm, 5 mm, 10 mm and 15 mm so as to measure arelationship between wind flow and noise. As shown in FIG. 11, the noisewas reduced and the wind flow was increased when the air-flow-directionlengths h1 and h2 differed from each other as compared to when theair-flow-direction lengths h1 and h2 were equal. Especially, when thedifference between h1 and h2 was 5 mm or 10 mm, the noise was the mostreduced with the same wind flow. In FIG. 11, a scale unit of thevertical axis of the graph is 1 dBA and a scale unit of the horizontalaxis is 10 m³/min.

While the air-flow-direction length of the outer circumferential wall 53was maintained to be larger than the air-flow-direction length of theinner circumferential wall 52 by 10 mm, a covering ratio of the outercircumferential wall 53 relative to the air-flow-direction downstreamside end of the cooling fan 21 (hereinafter referred to as an exteriorcovering ratio) was changed so as to measure a relationship between theexterior covering ratio, wind flow and noise.

As shown in FIG. 8, “the exterior covering ratio” is defined as apercentage (%) of h6/h3 when h6 is obtained by subtracting anair-flow-direction length h7 of the cooling fan 21 from the maximumair-flow-direction length h3 of the cooling fan 21. Theair-flow-direction length h7 of the cooling fan 21 is theair-flow-direction length of the air-flow-direction downstream side endof the cooling fan 21 extending from the air-flow-direction downstreamside end of the outer circumferential wall 53.

As shown in FIG. 12, it was found that the wind flow was the largestwhen the exterior covering ratio was in the range of 55 to 95%. In FIG.12, a scale unit of the vertical axis of the graph is 10 m³/min.

To increase the wind flow, the exterior covering ratio is preferably inthe range of 55 to 95%, more preferably 70 to 80%.

To reduce the noise, on the other hand, the exterior covering ratio ispreferably in the range of 70 to 95% as shown in FIG. 13. In FIG. 13, ascale unit of the vertical axis of the graph is 0.5 dBA.

As shown in FIG. 14A, when the air-flow-direction downstream side end ofthe outer circumferential wall 53 was positioned at a farther downstreamposition in the air flow direction than the air-flow-directiondownstream side end of the cooling fan 21, the flow of air radiallydischarged from the cooling fan 21 is interrupted, and the flow speed ofair passing through the space 55 provided between the innercircumferential wall 52 and the outer circumferential wall 53 isreduced. Also, the air that radially flows from the fan collides withthe outer circumferential wall 53, so that the air is partiallydelivered into the space. Presumably because of the above, a negativepressure is not easily generated within the space 55 when the exteriorcovering ratio exceeds 100%.

On the other hand, as shown in FIG. 14B, when at least theair-flow-direction downstream side end of the outer circumferential wall53 is positioned at a further upstream position in the air flowdirection than the air-flow-direction downstream side end of the coolingfan 21, the flow of air presumably passes through the space 55 with acertain speed, thereby generating a negative pressure within the space55.

From the above, the following findings have been made with respect tothe relationship between the interior covering ratio of the innercircumferential wall 52, the exterior covering ratio of the outercircumferential wall 53, the wind flow and the noise:

-   -   the difference between the air-flow-direction length h1 of the        inner circumferential wall 52 and the air-flow-direction length        h2 of the outer circumferential wall 53 is preferably 5 to 10 mm        to reduce the noise with the same air volume;    -   the exterior covering ratio of the outer circumferential wall 53        is preferably 55 to 95% in terms of increase in the wind flow,        the exterior covering ratio is more preferably 70 to 95% in        terms of reduction in the noise, and the exterior covering ratio        is more preferably 70 to 80% in terms of increase in the wind        flow; and    -   the interior covering ratio of the inner circumferential wall 52        is preferably 45 to 85% to increase the air volume.

[Characteristics of Cooling Unit 20]

(1)

The cooling unit 20 for a construction machine, which is a coolingdevice for use in the hydraulic excavator 1, includes: the cooling fan21; the shroud 40 for covering the outer circumferential side of thecooling fan 21; and the space 55 having the inner circumferential wall52 that is provided on the shroud 40 and adjacent to the outercircumference of the cooling fan 21. The space 55 increases the flow ofair blown by the cooling fan 21, by generating the negative pressurewith the air discharged from the cooling fan 21. The air-flow-directiondownstream side end of the outer circumferential edge of the cooling fan21 is positioned at a further downstream position in the air flowdirection than the air-flow-direction downstream side end of the innercircumferential wall 52.

In the cooling fan 20, the negative pressure is generated in the space55 when the cooling fan 21 is rotated to flow air, so that the flow ofair blown by the cooling fan 21 is increased. More specifically, whenone point within the space 55 is positioned between the vanes 21 a, airis suctioned by the negative pressure generated therein, andsubsequently the air is swept out by the vanes 21 a. Since theair-flow-direction downstream side end of the outer circumferential edgeof the cooling fan 21 is positioned at a further downstream position inthe air flow direction than the air-flow-direction downstream side endof the inner circumferential wall 52, the sufficient amount of air issupplied to the space 55 and the flow of air blown by the cooling fan 21is increased due to synergistic interaction between the air and thenegative pressure within the space 55. Thus, the flow of air flowing inthe vicinity of the cooling core 30 is increased, so that engine coolingperformance of the radiator 31 and the like of the cooling core 30 isenhanced.

(2)

When the ratio (percentage) between the air-flow-direction length of theportion covered by the shroud 40 and the inner circumferential wall 52on the outer circumferential edge of the cooling fan 21 and the wholeair-flow-direction length of the cooling fan 21 is referred to as theinterior covering ratio, the interior covering ratio is in the range of45 to 85%. The flow of air blown by the cooling fan 21 is sufficientlyincreased by setting the interior covering ratio in an appropriaterange. Thus, cooling capability is enhanced even when the rotation speedof the cooling fan 21 is the same as conventional. Even when therotation speed of the cooling fan 21 is reduced, the same coolingcapability can be obtained.

(3)

The space 55 is formed by the ring 51. The ring 51 includes the innercircumferential wall 52 adjacent to the outer circumference of thecooling fan 21 and the outer circumferential wall 53 extending towardthe air-flow-direction downstream side further than the innercircumferential wall 52. The air-flow-direction downstream side end ofthe outer circumferential edge of the cooling fan 21 is positioned at afurther downstream position in the air flow direction than theair-flow-direction downstream side end of the inner circumferential wall52. When the cooling fan 21 is rotated to flow air, negative pressure isgenerated in the space 55 provided between the inner circumferentialwall 52 and the outer circumferential wall 53 of the ring 51. Thus, theflow of air blown by the cooling fan 21 is increased as described above.

(4)

The ring 51 is made from a member different from the shroud 40. Sincethe ring 51 is attachable to the shroud 40, an appropriate ring 51 canbe selected suitably for the arrangement of the shroud 40 and thecooling fan 21.

(5)

The ring 51 includes the annular base 54 for connecting the innercircumferential wall 52 with the outer circumferential wall 53. Sincethe ring 51 is an integral member formed by the inner circumferentialwall 52, the outer circumferential wall 53 and the base 54, it is easyto manufacture and manage the ring 51.

(6)

The inner circumferential wall 52 and the outer circumferential wall 53are cylindrical portions extending in parallel to the air flowdirection. Thus, it is easy to manufacture the ring 51.

(7)

The cooling fan 21 is driven to rotate by the engine 6 a included in aconstruction machine such as a hydraulic excavator. Since the coolingfan 21 is rotated by the rotation of the engine 6 a, the arrangement canbe simplified.

Second Exemplary Embodiment

Next, a second exemplary embodiment of the invention will be describedbelow. In the following description, the same components as thosedescribed above will be indicated by the same reference numerals and thedescription thereof will be omitted.

In the first exemplary embodiment, the inner circumferential wall andthe outer circumferential wall are provided as the annular ring 51surrounding the cooling fan 21.

In the cooling device according to the second exemplary embodiment, aplurality of wall components 112 are provided as shown in FIG. 15, inplace of the consecutive ring 51. More specifically, the wall components112 are combined around the rotation shaft of the cooling fan 21 tosurround the cooling fan 21, which is different from the first exemplaryembodiment.

As shown in FIG. 8 according to the first exemplary embodiment, the wallcomponents 112 respectively include the inner circumferential wall 52and the outer circumferential wall 53, and the air-flow-directiondownstream side end of the cooling fan 21 is positioned at a furtherdownstream position in the air flow direction than theair-flow-direction downstream side end of the inner circumferential wall52.

The interior covering ratio is in the range of 45 to 85%, preferably 60to 70% as in the first exemplary embodiment.

The wall components 112 are laid around the rotation shaft of thecooling fan 21 on an outer surface of the case 41 of the shroud and arefixed by a bolt, an adhesive or weld.

Incidentally, although a slight clearance is provided between adjacentwall components 112, cooling efficiency as described in the firstexemplary embodiment is hardly impaired because substantially the wholeouter circumference of the cooling fan 21 is surrounded by the innercircumferential wall 52 and the outer circumferential wall 53 of each ofthe wall components 112. To ensure the efficiency more reliably, theclearance between the adjacent wall components 112 may be filled in witha joint member, paste or weld after fixing the case 41 of the wallcomponents 112.

While FIG. 11 shows four wall components, the number of the wallcomponents is not limited thereto but may be approximately two to six.

According to the second exemplary embodiment, even when the coolingdevice includes a large cooling fan 21 used for a large constructionmachine, the inner circumferential wall 52 and the outer circumferentialwall 53 can be formed to surround substantially the whole circumferenceof the cooling fan 21.

Other Exemplary Embodiments

Though the exemplary embodiments of the invention have been describedabove, the invention is not limited thereto, but includes modificationsas long as such modifications are compatible with the invention.

(A)

Though the ring 51 is a single annular member in the first exemplaryembodiment, the invention is not limited thereto. The ring may be formedby annularly arranging inner circumferential walls and outercircumferential walls consecutively by combining a plurality of members.For example, as shown in FIG. 17, a consecutive ring can be formed bycombining ends of two semi-annular members 113 each having the innercircumferential wall 52 and the outer circumferential wall 53.

(B)

In the above-described exemplary embodiments, the inner circumferentialwall and the outer circumferential wall extend in parallel in the airflow direction. However, the invention is not limited thereto.

For example, a ring 61 shown in FIG. 17 includes an innercircumferential wall 62, an outer circumferential wall 63 and a base 64.The inner circumferential wall 62 is positioned on the edge of theopening of the case 41. The outer circumferential wall 63 is positionedat a further radially outward position than the inner circumferentialwall 62, and an annular space 65 is provided therebetween. The innercircumferential wall 62 and the outer circumferential wall 63 areconcentric to define a trumpet shape (a bottom-widened shape) of which adiameter increases as extending to the downstream side in the air flowdirection. Incidentally, only either one of the inner circumferentialwall and the outer circumferential wall may have a trumpet shape.

In such an exemplary embodiment, the same advantages can be attained asin the above-described exemplary embodiments. Further, this exemplaryembodiment can reduce the noise by suppressing turbulence.

(C)

For example, a ring 71 shown in FIG. 18 includes an innercircumferential wall 72, an outer circumferential wall 73 and a base 74.The inner circumferential wall 72 is positioned on the edge of theopening of the case 41. The outer circumferential wall 73 is positionedat a further radially outward position than the inner circumferentialwall 72, and an annular space 75 is provided therebetween. The innercircumferential wall 72 and the outer circumferential wall 73 areconcentric to extend in parallel in the air flow direction.Specifically, a taper portion 72 a is provided on a distal end of theinner circumferential wall 72. A taper portion 73 a is provided on adistal end of the outer circumferential wall 73. The diameters of thetaper portions 72 a and 73 a gradually increase toward the downstreamside in the air flow direction. Incidentally, only either one of theinner circumferential wall and the outer circumferential wall may havethe taper portion.

In such an exemplary embodiment, the same advantages can be attained asin the above-described exemplary embodiments. Further, this exemplaryembodiment can reduce the noise by suppressing turbulence.

(D)

In the above-described exemplary embodiments, the inner circumferentialwall and the outer circumferential wall are formed by an integratedmember.

However, the invention is not limited thereto.

For example, a ring 81 shown in FIG. 19 is formed by two separatemembers of an inner circumferential wall 82 and an outer circumferentialwall 83. An annular space 85 is provided between the innercircumferential wall 82 and the outer circumferential wall 83. The innercircumferential wall 82 includes a cylindrical portion 82 a and a fixedportion 82 b. The fixed portion 82 b is fixed to the case 41 by a boltor weld. The outer circumferential wall 83 includes a cylindricalportion 83 a and a fixed portion 83 b. The fixed portion 83 b is fixedto the case 41 of the shroud 40 by a bolt or weld.

In such an exemplary embodiment, the same advantages can be attained asin the above-described exemplary embodiments.

(E)

In the above-described exemplary embodiments, the inner circumferentialwall and the outer circumferential wall are formed by members differentfrom the shroud. However, the invention is not limited thereto.

For example, a ring 91 shown in FIG. 20 is formed by an innercircumferential wall 92 formed by bending the inner circumferential edgeof the case 41 and an outer circumferential wall 93. An annular space 95is provided between the inner circumferential wall 92 and the outercircumferential wall 93. The outer circumferential wall 93 includes acylindrical portion 93 a and a fixed portion 93 b. The fixed portion 93b is fixed to the case 41 of the shroud 40 by a bolt or weld.

In such an exemplary embodiment, the same advantages can be attained asin the above-described exemplary embodiments.

(F)

The ring may be integrated with the shroud according to an aspect of theinvention. As shown in FIG. 21, a ring 101 is integrated with the case41 of the shroud. An inner circumferential wall 102 is provided on theinner circumferential edge of the case 41 and an outer circumferentialwall 103 is provided on the outer surface of the case 41. Further, aspace 105 for generating negative pressure is provided between the innercircumferential wall 102 and the outer circumferential wall 103.

In such an exemplary embodiment, the case 41 of the shroud and the ring101 may be made of resin by a method such as injection molding. Such ashroud is favorably adoptable for a small construction machine whichonly requires a certain level of durability.

In such an exemplary embodiment, the same advantages can be attained asin the above-described exemplary embodiments. Further, the load ofassembling work can be reduced by reduction of the number of parts, andthe weight of a construction machine can be reduced.

(G)

In the above-described exemplary embodiments, the cooling fan 21 isexemplarily rotated directly by the engine 6 a as shown in FIG. 4.However, the invention is not limited thereto.

For example, the cooling fan may be rotated by a hydraulically-actuatedmotor provided in the vicinity of the cooling core such as the radiator.

Such an arrangement can be designed without concern for influence byvibration of the engine unlike an arrangement for the cooling fanrotated directly by the engine. Thus, the clearance G between thecooling fan 21 and the inner circumferential wall 52 of the ring 51provided on the shroud 40 can be minimized. Consequently, air in thevicinity of the shroud 40 can flow more smoothly, thereby reducing thenoise and enhancing cooling efficiency of the cooling core.

Alternatively, the cooling fan may be rotated by an electric motor.

(H)

In the above-described exemplary embodiments, the intake cooling unit 20is exemplarily used, in which the cooling fan 21 is provided on thedownstream side of the cooling core 30 in the air flow direction asshown in FIG. 4. However, the invention is not limited thereto.

For example, as shown in FIG. 22, the invention is applicable to aso-called blowoff cooling unit 20 for sending air from the engine 6 a tothe cooling core 30 such as the radiator by the cooling fan 21.

In other words, even in the blowoff cooling unit 20, wind flow isincreased as in the first exemplary embodiment by providing the ring 51within the shroud 40, so that the cooling core 30 can be efficientlycooled and the noise can be reduced.

(I)

In the above-described exemplary embodiments, the cooling fan 21 isexemplarily described as an axial-flow fan as shown in FIG. 6. However,the invention is not limited thereto.

For example, the cooling unit may include other blast fan such as asirocco fan and an obliquely axial-flow fan.

(J)

In the above-described exemplary embodiments, the radiator 31, the oilcooler 32 and the aftercooler 33 are exemplarily used as a heatexchanger of the cooling core 30. However, the invention is not limitedthereto.

For example, only radiator may be used as a cooling core positionedopposite to the cooling fan according to the aspect of the invention.Alternatively, other heat exchangers may be used alone or incombination.

(K)

In the above-described exemplary embodiments, the hydraulic excavator 1is exemplarily described as a construction machine including the shroud40 of the cooling fan 21 according to the aspect of the invention asshown in FIG. 1. However, the invention is not limited thereto.

For example, the invention is also applicable to other constructionmachine such as a wheel loader or work machine such as a forklift inaddition to the hydraulic excavator.

(L)

The above-described exemplary embodiments may be adopted alone or incombination.

INDUSTRIAL APPLICABILITY

A cooling device and a construction machine and work machine includingthe same according to the aspect of the invention can sufficientlyincrease flow of air discharged from a cooling fan without increasingrotation speed of the cooling fan. Thus, the invention is applicable tovarious work machines equipped with the cooling device.

1. A cooling device, comprising: a cooling fan; a shroud provided at anouter circumferential side of the cooling fan; an inner circumferentialwall provided on the shroud and adjacent to the outer circumference ofthe cooling fan so as to surround the cooling fan; and an outercircumferential wall provided to surround the inner circumferentialwall, an air-flow-direction downstream side end of the outercircumferential wall being positioned at a further downstream positionin an air flow direction than an air-flow-direction downstream side endof the inner circumferential wall, wherein the cooling fan is rotatablein a space on a radially inner side of the inner circumferential wall,and the air-flow-direction downstream side end of the outercircumferential wall is positioned at a further upstream position in theair flow direction than an air-flow-direction downstream side end of thecooling fan.
 2. The cooling device according to claim 1, wherein atleast one of the inner circumferential wall and the outercircumferential wall is a ring that is consecutively provided around arotation shaft of the cooling fan.
 3. The cooling device according toclaim 1, wherein an exterior covering ratio is in a range of 55 to 95%,the exterior covering ratio being defined as a ratio between: anair-flow-direction length of a portion covered by the shroud and theouter circumferential wall; and a maximum air-flow-direction length ofthe cooling fan in the air flow direction of the cooling fan.
 4. Thecooling device according to claim 3, wherein the exterior covering ratiois in a range of 70 to 95%.
 5. The cooling device according to claim 4,wherein the exterior covering ratio is in a range of 70 to 80%.
 6. Thecooling device according to claim 1, wherein an interior covering ratiois in a range of 45 to 85%, the interior covering ratio being defined asa ratio between: an air-flow-direction length of a portion covered bythe shroud and the inner circumferential wall; and a maximumair-flow-direction length of the cooling fan in the air flow directionof the cooling fan.
 7. The cooling device according to claim 1, whereinat least one of the inner circumferential wall and the outercircumferential wall is integrated with the shroud.
 8. The coolingdevice according to claim 1, wherein at least one of the innercircumferential wall and the outer circumferential wall is formed by amember different from the shroud.
 9. The cooling device according toclaim 8, further comprising: an annular base connecting the innercircumferential wall to the outer circumferential wall.
 10. The coolingdevice according to claim 1, wherein at least one of the innercircumferential wall and the outer circumferential wall includes acylindrical portion extending in parallel to the air flow direction. 11.The cooling device according to claim 1, wherein at least one of theinner circumferential wall and the outer circumferential wall includes adiameter-expanded portion of which an inner diameter increases towarddownstream in the air flow direction.
 12. A construction machine or awork machine, comprising the cooling device according to claim 1.